hi,
While creating a toggleButtonBar any one of the butttons is
being selected by default.
Can anyone say how to make no buttons being selected in the
toggleButtonBar.
i tried with selectedIndex=-1 but its not working

There's a
toggleOnClick property that lets the user select and
deselect the same button, so you can set thisproperty to true and
then try to set the selectedIndex to -1.

According to the documentation, the toggleOnClick property:
Specifies whether the currently selected button can be
deselected by the user. By default, the currently selected button
gets deselected automatically only when another button in the group
is selected. Setting this property to true lets the user deselect
it. When the currently selected button is deselected, the
selectedIndex property is set to -1.

I think you are going to need to use a custom component which
extends from ToggleButtonBar, because you will need to call a
function named hiliteSelectedNavItem( index:int ) to do that.

Here's the documentation on the ToggleButtonBar, there you
will see the method i just mentioned, but since it is protected you
will need to create a custom component, extend the ToggleButtonBar
and then have it call the function.